Curing catalyst

The curing of organo-modified polysiloxane resins obtained by partial reaction of alkoxypolysiloxanes with organic polyols is accelerated by a catalyst prepared by reacting from 1 to 2 mol of a polycarboxylic anhydride with 1 mol of a compound of the formula in which R and R are identical or different and are groups, and R is an alkylene, cycloalkylene or phenylene group, subsequently reacting this intermediate with from 0.4 to 6 mol of Ti(OR )4 (R is an alkylene group having 1 to 6 carbon atoms) with removal of the alcohol R OH, it being possible to terminate the reaction after at least 25% of the theoretical amount of R OH has been liberated. The catalyst according to the invention is stable to hydrolysis. If it is used for the curing of thermocurable polyester-polysiloxane resins, coatings are obtained which have high hydrolysis resistance and weathering resistance.